Histone deacetylase (HDAC) activity is involved in a number of disease states, for example, cancer (Marks et al., Nature Reviews, 1, 194-202, 2001), cystic fibrosis (Li. S. et al, J. Biol. Chem., 274, 7803-7815, 1999), Huntington's chorea (Steffan, J. S. et al., Nature, 413, 739-743, 2001), and sickle cell anaemia (Gabbianelli. M. et al., Blood, 95, 3555-3561, 2000).
Thus, studies on the regulation of transcription of histone acetylases (HATs) and histone deacetylases (HDACs), which are involved in chromatin structure, have been actively conducted. It is known that histone acetylases are enzymes that catalyze the acetylation of N-terminal histone tails to cause an unstable chromatin structure, whereas histone deacetylases remove acetyl groups from histones to stabilize chromatin structure so as to interfere with the accession of transcription factors to target genes, thereby inhibiting transcriptional activity. Acetylation of histones is regulated by histone deacetylases that catalyze the removal of acetyl groups from the lysine residues of histones. If acetyl groups are attached to histone proteins, the expression of proteins that are involved in the suppression of cancer will be stimulated, but if the acetyl groups are removed from histone proteins, the expression of proteins that are involved in the suppression of cancer will be inhibited. Thus, inhibition of histone deacetylase (HDAC) activity leads to arrest of the cell cycle, inhibition of blood vessel formation, immune regulation, cell death, etc. Namely, if the enzymatic activity of histone deacetylases is inhibited, the activity of factors associated with the survival of cancer cells in vivo will be inhibited, and the activity of factors associated with the death of cancer cells will be increased, whereby the death of cancer cells will be induced. Recent studies on histone modification enzymes revealed that histone deacetylases play an important role in tumor formation. 11 members-cloned HDAC, which is expressed from humans, is over-expressed in several tumor cells, and in this state, the expression of tumor suppressors such as p53 and p21 is inhibited, but tumor activators, such as hypoxia-induced factor-1 and vascular endothelial growth factor (VEGF), are up-regulated. Particularly, a decrease in tubulin acetylation that is mediated by histone deacetylases was observed in patients suffering from neurodegenerative diseases such as Alzheimer's disease.
Thus, it has been recognized that inhibition of histone deacetylase activity can be applied for the treatment of cancer and other diseases. In fact, inhibition of histone deacetylase activity by a specific inhibitor results in changes in the acetylation of proteins at the molecular and cellular levels, the expression of a specific gene, and the morphology, proliferation and migration of cells.
Histone deacetylase inhibitors found to date can be divided, according to their structure, into four categories: 1) short-chain fatty acids (e.g., butyric acid and valproic acid); 2) hydroxamic acids (e.g., trichostatin A, SAHA and oxamflatin); 3) cyclic peptides (e.g., depsipeptide and Trapoxin); and 4) benzamides (e.g., MS-275, MGCD 0103, and CI-994) (International Journal of oncology 33, 637-646, 2008). These histone deacetylase inhibitors (SAHA, pyroxamide, scriptide, oxamfiatin, NVP-LAQ-824, CHAPs and MS-275) effectively induce the growth inhibition, differentiation and apoptosis of various transformed cells in animal models and media (Marks, P. A et al., Curr Opin. oncol. 2001, 13, 477-483), and HDAC inhibitors, such as SAHA, NVP-LAQ-824 and MS-275, have been evaluated in clinical trials for the treatment of various cancer diseases (Johnstone. R. W Nat. Rev. Drug Discov. 2002, 1, 287-299). Typical examples of HDAC inhibitor compounds that are currently known include hydroxamate compounds, such as SAHA (U.S. Pat. No. 771,760, Zolinza, vorinostat), PXD101 (WO 02/30879, Belinostat) and LBH589 (WO 02/22577, Panobinostat), and benzamide compounds, such as MS275 (EP 847992) and MGCD0103 (WO 04/69823). Of these compounds, SAHA, a typical HDAC inhibitor, was approved in October 2006 by the US FDA and has been used for the treatment of cutaneous T-cell lymphoma (CTCL). The range of diseases to which SAHA can be applied is being additionally expanded, but it is known that the effect of SAHA is insufficient (Cancer Res 2006, 66, 5781-5789).
Although many HDAC inhibitors have been reported to date, there has been a continuous need for a more selective, more effective HDAC inhibitor which overcomes the above-described disadvantage (Mol Cancer Res, 5, 981, 2007).
The present inventors have conducted many studies to develop agents for treating the above-mentioned diseases and, as a result, have developed derivatives which are completely different from known compounds, thereby completing the present invention.